<p>I am not clear on what you are asking but only a parent can obtain a parent PLUS loan (unless the step has adopted the student). I think the PLUS loan would consider the parents income to determine loan eligibility - regardless of tax filing.
[Direct</a> Loans—Parent PLUS Information](<a href=“http://www.direct.ed.gov/parent.html]Direct”>http://www.direct.ed.gov/parent.html)</p>